Blauwwind and The Rich North Sea Oyster Pilot
Provide a Kick-Start for a Population of Ostrea edulis

Photo: with copyright

The Netherlands
Joint Project – Blauwwind and The Rich North Sea Oyster Pilot

General introduction

The Rich North Sea

Offshore wind farms (OWFs) can have a positive effect on marine biodiversity. The aim of the Rich North Sea programme is to enhance nature within OWFs in the North Sea by developing and implementing biodiversity enhancement measures. It therefore wants to:

  1. develop reefs within pilot projects in the North Sea
  2. build a strong scientific knowledge base about ecosystem restoration
  3. to create a Nature Development Toolbox containing the most required information on nature development in wind farms in the Dutch North Sea, which will be a guide for future projects.


Blauwwind is the consortium (of Shell, Van Oord, Eneco, Diamond Generating Europe and Partners Group) that develops Offshore Wind Farm (OWF) Borssele III & IV. This OWF will supply green energy for 825.000 Dutch households and has an installed capacity of 731.5 MW. The OWF is situated about 55 km from the port of Vlissingen and generates our sustainable energy. The OWF also harbours potential for nature development on the scour around monopiles. As responsible OWF developer Blauwwind will be executing experiments to investigate how nature development can be further encouraged making use of the flat oyster.


Blauwwind established a detailed Nature Inclusive Design (NID) plan for research on the parameters needed for the habitat of the flat oyster in wind farms Borssele II and IV, approved by Rijkswaterstaat in their capacity as regulator. The Rich North Sea and Blauwwind have joined forces to expand this plan to gain more understanding of the influences of habitat conditions on biodiversity and how we can stimulate flat oyster reef development. This project has international potential because it can be implemented on foundations of all wind turbines in more or less the same conditions.


The aim of this joint project is to provide a kick-start for a population of native flat oyster (Ostrea edulis) within the offshore Borssele III and IV wind farm and learn about the effects of different materials on their settlement and biodiversity in general.

Research questions

The research questions from the originating NID Plan will be investigated as a baseline. The collaboration between Blauwwind and De Rijke Noordzee has led to an expansion upon these originating research questions. 

The experimental set up has been conducted in a manner that during the 8 year lasting experiment, the following research questions can be investigated:

  1. What is the survival and growth rate of flat oysters?
  2. Do the flat oysters produce larvae?
  3. Do the flat oysters stay free of the parasite Bonamia?
  4. Do oyster larvae settle on different scour protection substrates (armour layer, filter layer and empty shells)?
    1. Do they have a preference for any type?
    2. Can the oyster spat and/or larvae also be found in the control zone?
  5. How is biodiversity in general developing on the different substrate variations?
  6. Can patterns be found in oyster larvae settlement or species-specific responses in relation to current directions?
  7. Is the species data found by ROV (remotely operated vehicle) video and photo analyses correlated to the eDNA data? Which species are not found or only found by a certain method?
  8. How fast does succession of a hard substrate community occur in the Borssele area?


Figure 1 shows the location of the Borssele wind farm area, about 25 km off the coast of Zeeland. The yellow areas in Figure 2 indicate areas which represent suitable for the oyster experiments. One of these will be utilised as treatment site where the other serves as a control sites. The depth in these areas is between 25 and 38 meters relative to LAT and sand wave migration speeds are lower than 0.5 meter per year (Smaal et al., 2017).

Figure 1. Borssele Wind Farm Zone (Source: NID plan Blauwwind)
Figure 2. Suggested areas (yellow) within Borssele III and IV to perform the experiment. (Source: NID plan Blauwwind)
Figure 3. Schematic outline of the experimental set up (topview): 4 set ups, each with 4 experiments (grading (F/C) x clean shells (S)) in different flow directions (1,2) around the wind turbine and accompanied by a rack of live oysters. At another location with similar environmental conditions, 4 turbines will be monitored for control (grading in different flow directions and addition of clean shells, but without addition of live oysters). (Source: NID plan Blauwwind 2019)

Using Blauwwind’s NID Plan as a basis, an experiment was designed at eight different monopile sites. Four sites are used as control site while a total of total 2400 flat oysters will be installed in cages on the scour protection at four other experimental sites. As depicted in Figure 3, all locations consist of three different substrates where oyster larvae could potentially settle on. These are the armour (coarse rock) layer of scour protection, the filter (finer rock) layer and clean empty shell material that is placed on top of the scour protection in different orientations compared to the main current direction. The shell layer will be deposited during the T1 in July 2021, so that oyster larvae that are released in the water around that time have clean shell material available for settlement. Also, clean shell material will be placed inside the oyster cages every trip, functioning as ‘spat collectors’ with the purpose of providing readily collectable settlement material for juvenile oysters.

Monitoring and planning

Four monitoring trips are planned between October 2020 and July 2028. The first one in combination with installation of the oyster racks and the last one includes decommissioning. Different monitoring techniques are used to gain all data needed to answer the questions. An ROV will be used to create video and photo material for biodiversity and possibly oyster spat analysis of the areas around the monopiles. eDNA sampling will be used to investigate if native flat oysters are present in the local seawater. Water will also be sieved to verify the presence and concentration of oyster larvae per location. The oyster cages will be lifted to record survival rates and measure the growth of the adult oysters.

Table 1 shows the measured parameters and planning of the project. After the first installation (T0) campaign a field report will be written by the scientist. After the T1 and T3 campaigns intermediate scientific reports will be written. At the end of the project (T8), a detailed scientific analysis will be made available.

Table 1. Scope of the monitoring activities in the Blauwwind project.

T0October 20203
  • Oyster sizes (mm)
Install oyster cages and measure length and width of the adult oysters 
  • Total biodiversity by ROV within and in addition to the treatments
ROV video and photo survey. Coverage categories photos: 0-25, 25-50, 50-75 and 75-100%. Abundance categories video material: 1-10, 10-100, 100-500, >500 individuals or colonies.
  • Biodiversity by eDNA analysis
1 water sample per location
June 2021
July 2023
July 2028
  • Total biodiversity by ROV within and in addition to the treatments
ROV video and photo survey. Coverage categories photos: 0-25, 25-50, 50-75 and 75-100%. Abundance categories video material: 1-10, 10-100, 100-500, >500 individuals or colonies.
  • Oyster survival (dead/alive)
  • Oyster sizes (mm)
  • Bonamia presence/absence
  • Reproduction yes/no
  • Spat density on spat collectors
Measure oyster sizes. Bring dead ones, subsamples and spat collectors back to shore for analysis in lab (Bonamia presence by DNA, reproduction status – gonad development and from the spat collectors density spat/shell). 
  • Biodiversity by eDNA analysis
1 water sample per location using pump water from larvae analysis
  • Density of flat oyster larvae
Filter 200L water samples and use microscope to identify species (if possible) and estimate density

Third Parties Involved 

Eurofins AquaSense executes scientific monitoring and reporting, including analysis of photo/video material and lab work with assistance of The Rich North Sea. They also arrange measurement materials for the monitoring trips.

Van Oord Offshore Wind is the chosen offshore contractor and will arrange installation of assets and facilitate monitoring expeditions. They arrange the ROV and pilot, instruments to take water samples, cages, spat collectors and shell materials. They are also responsible for the procurement and transport of parasite-free flat oysters.


The main challenges and mitigation measures for this project are identified in table 2.

Table 2. Challenges for the joint Blauwwind and The Rich North Sea project and the mitigation measures.

ChallengesMitigation measures
Bonamia-free oysters are needed for the project
  • Have information about different sources of Bonamia-free oysters
  • Approval from authorities to use source material from other countries
Structural integrity of oyster racks 
  • Calculate structural integrity beforehand  
  • Use materials and corrosion allowance that can withstand North Sea conditions for at least 8 years
  • Inspection and Replacement of baskets after each campaign
Installation in North Sea conditions
  • Weather risk is included in installation contract
  • Make arrangements with scientific operator about weather risk, contingency allowance 
  • Create a bigger window for the installation/monitoring campaign
  • Temporary storage of oysters with VOOW
  • Monitoring of weather and keep in close contact to oyster producer
 Gaining valuable research and ecological output 
  • Experimental setup of scour protection designs with control (NID plan)
  • Different types of settlement substrate are present
  • Right timing of the provision of suitable and clean substrate for settlement of larvae (July)
  • T0 monitoring and biodiversity monitoring
COVID-19 effects
  • Test passengers two days before boarding, after which they stay quarantined 
  • Keep 1.5 meters distance from each other
Obtain clear videos and images from ROV 
  • Check specifications beforehand, check reference material
  • Monitor the quality of the images during the survey


Blauwwind, Wind Farm Borssele III & IV, Nature Inclusive Design Plan version 9 (2019), Wind Farm Site Decision regulatory basis 2.15. Document number: BW-PRO-00249

Smaal, A., Kamermans, P., Kleissen, F., Duren, L. van, & van der Have, T. (2017). Flat oysters on offshore wind farms (Issue April).